This invention relates to a gas chromatograph and a method of using it selectably in split and wide bore injection modes.
When high accuracy gas chromatographic analyses are desired, it has been known to use a gas chromatograph in a so-called split mode wherein the injected sample is split and only a fraction thereof is introduced into the capillary column.
When it is desired to detect a component which is contained only by a small quantity, on the other hand, a so-called wide bore injection analysis is much more suitable for accurate analysis. In a wide bore injection analysis, therefore, a splitless injection is more often applied than the split injection. Thus, prior art apparatus for gas chromatography were provided separately with both a unit for split mode analyses and another unit for wide bore injection analyses. Whenever the mode of analysis was to be changed with such an apparatus, these units including both a column and a sample injection chamber had to be exchanged and the pipes reconnected.
Sample injection chambers for use in a wide bore injection analysis are distinguishable from those for use in a split mode analysis only in that there is no split piping line connected thereto. It may be thought, therefore, that a sample injection chamber for split mode analysis can be used for a wide bore injection analysis simply by blocking the split piping line such that the sample will not split out therethrough. This, however, is not so for the following reasons. Firstly, since sample injection chambers and columns are generally unitized, the valve to be used for blocking the split line must be located near its outlet. Secondly, the split piping line must be provided with a trap for removing the sample from the gas which is being split out. For the reason mentioned above, there results a relatively large dead space between the sample injection chamber and the valve for blocking the split piping line. In a wide bore injection analysis, a relatively large part of the sample tends to accumulate and stay in this dead space, failing to be transported into the column. This is the reason why the units as a whole had to be exchanged and the pipes reconnected in the case of a prior art gas chromatographic apparatus whenever the mode of analysis was switched between the split mode and the wide bore injection mode.
The present invention was accomplished in view of this problem. In other words, it is an object of the present invention to provide a gas chromatograph which can be easily switched between a split mode analysis and a wide bore injection analysis.